The evolution of computer and electronic systems has demanded ever-increasing levels of performance. In most regards, the increased performance has been achieved by electronic components of ever-decreasing physical size. The diminished size itself has been responsible for some level of increased performance because of the reduced lengths of the paths through which the signals must travel between separate components of the systems. Reduced length signal paths allow the electronic components to switch at higher frequencies and reduce the latency of the signal conduction through relatively longer paths.
One technique of reducing the size of the electronic components is to condense or diminish the space between the electronic components. A diminished size also allows more components to be included in a system, which is another technique of achieving increased performance because of the increased number of components.
A particularly effective approach to condensing the size between electronic components is to attach multiple semiconductor integrated circuits or “chips” on printed circuit boards, and then stack multiple printed circuit boards to form a three-dimensional configuration or module. Interconnectors are extended vertically, in the z-axis dimension, between the vertically stacked printed circuit boards, each of which is oriented in the horizontal x-axis and y-axis dimensions. The interconnectors, in conjunction with conductor traces of each printed circuit board, connect the chips of the module with short signal paths. The relatively high concentration of chips, which are connected by the three-dimensional, relatively short length signal paths, are capable of achieving very high levels of functionality.
The z-axis interconnectors contact and extend through plated through holes or “vias” formed in each of the printed circuit boards. The chips of each printed circuit board are connected to the vias by conductor traces formed on or within each printed circuit board. The vias are formed in each individual printed circuit board of the three-dimensional modules at similar locations, so that when the printed circuit boards are stacked in the three-dimensional module, the vias of all of the printed circuit boards are aligned vertically in columns along the z-axis. The z-axis interconnectors are then inserted in the column of vertically aligned vias to establish an electrical contact and mechanical connection between the circuit boards, thus assembling the module.
A number of different types of z-axis interconnectors have been proposed. One particularly advantageous type of z-axis interconnector is known as a “twist pin.” Twist pins are typically of a very small size. The most common sizes are about 0.0050, 0.0100 and 0.0150 in. in diameter. The typical length of a twist pin is about 1 to 1.5 inches. The weight of a typical four-bulge twist pin is about 0.0077 grams, making it so light that handling the twist pin is difficult. It is not unusual that a complex module formed by a 4 in. by 4 in. printed circuit board may require the use of as many as 22,000 twist pins. Thus, the relatively large number of twist pins necessary to assemble each three-dimensional module makes it necessary to insert and interconnect the circuit boards quickly and efficiently.
Assembling large numbers of twist pins or other z-axis interconnectors in three-dimensional circuit modules has previously been accomplished using multiple machines to accomplish part of the assembly required. For example, sorting and aligning the twist pins so that they may be inserted in the column of aligned vias has been performed using one type of machine, but the functionality of the machine still required constant operator attention and frequent operator intervention. Another function accomplished by another machine involved delivering the twist pins pneumatically to the via columns. This machine required the operator to view each column of aligned vias with a microscope to determine whether the twist pin was properly inserted, and when an insertion error was encountered, manually insert the twist pin. Pulling the twist pins from the initially inserted position was accomplished by a third type of machine, and a fourth machine was required to cut the leader portion of the twist pin. Each of these machines had to be controlled separately by specific operator actions.
Coordinating separate machines with one another during an entire twist pin assembly cycle is tedious activity for the machine operator. Furthermore, because the operation of the different machines are independent of one another, the functionality of one machine may adversely influence the ability of the other machine to achieve its desired functionality. Even under the best of circumstances, assembling z-axis interconnects such as twist pins into three-dimensional circuit modules has been relatively slow and time-consuming, and therefore inefficient and expensive. The inefficiencies and costs associated with such actions have created an impediment to using three-dimensional circuit modules with z-axis interconnects.